The present invention relates to a chromatographic separation method of separating carbohydrates, especially sugars, from a mixture including the same. The mixture to be treated in accordance with the present invention is typically a biomass-derived solution including carbohydrates/sugars. Especially, the invention provides a chromatographic separation method of recovering mannose with high purity from biomass-derived solutions, such as spent sulphite pulping liquors. Mannose can be recovered in a crystalline form or in the form of a solution. The claimed process of recovering mannose is based on the use of a combination of a Ba2+ form resin and a resin in other than Ba2+ form as the separation resin, whereafter mannose is crystallized, if desired. In connection with the separation process of the invention, xylose and arabinose products can also be obtained as by-products, depending on the composition of the starting biomass-derived solution.
Mannose is useful e.g. for various pharmaceutical applications. It can be used as a starting material or raw material for various pharmaceutical products. Mannose is also therapeutically useful in the treatment of urine infections and intravenous inflammation conditions. In food technology, mannose is useful e.g. for so-called Positech applications (GMO-testing of food products).
Mannose is also useful as the raw material for the production of mannitol, which has various pharmaceutical applications.
Mannose can be recovered from wood resources, where mannose is present as a mixture with other carbohydrates and lignin components. In wood and other plant-based material, mannose typically occurs in polymeric form, such as hemicellulose, most frequently as a heteropolymer with glucose and/or galactose in glucomannans, galactoglucomannans and galactomannans. Spent liquors obtained from conifer wood-pulping processes are especially rich in mannose. Mannose has also been recovered from vegetable ivory nuts and specific seaweeds.
The recovery of mannose with high purity from plant-based material has presented a problem in the state of the art.
Jones, J. K. N and Wall, R. A. (Canadian Journal of Organic Chemistry 38 (1960), pp. 2290 to 2294) have described a process for the separation of sugars from synthetic sugar mixtures and plant extracts using ion-exchange resins. The process relates to the separation of monosaccharide mixtures, including D-mannose and D-mannitol, using neutral salt forms of sulphonic acid type ion-exchange resins. The resin Dowex 50W X8 in Ba2+ form has been used as the separation resin.
Larsson, L. I and Samuelsson, O. (Acta Chemica Scandinavica 19 (1965), pp. 1357 to 1364) describe an automatic procedure for the separation of monosaccharides present in wood hydrolysates using ion exchange resins. The separation of 16 monosaccharides, including D-mannose, has been studied by partition chromatography on strongly basic anion exchange resins in the sulphate form using ethanol as the eluant.
Furthermore, the utilization of ion exchangers for the isolation of monosaccharides has been studied with the aim to examine the behaviour of sugars on columns containing a bisulfite saturated resin. For example, an anion exchanger (Amberlite IRA-400) in the bisulphite form has been used to separate fructose, glucose and mannose. As a practical result of this study, an improved method for the determination of reducing sugars in sulphite waste liquor is proposed.
The interactions occurring between aluminium oxide and aqueous solutions of monosaccharides, including D-mannose have also been studied. It is suggested that by proper choice of alumina, separation of sugars can be easily and quickly achieved on a preparative as well as analytical scale.
It is also known to recover mannose from various sources through mannose derivatives. Fujita, T and Sato, T in Bull. Chem. Soc. Japan 33 (1960) 353 disclose the recovery of D-mannose through N-phenyl-D-mannopyranosylamine. It is recited that N-phenyl-D-mannopyranosylamine is so stable and insoluble in water that it was recommended for the isolation of D-mannose even from very impure raw materials.
Herrick, F. W., Casebier, R. L., Hamilton, J. K. and Wilson, J. D. (xe2x80x9cMannose chemicalsxe2x80x9d, Applied Polymer Symposium No. 28 (1975), pp. 93 to 108) disclose a study relating to the development of an economic process for recovering mannose or its derivatives from wood resources, such as a spent sulphite liquor, where mannose is a major component of mixtures containing other carbohydrates and lignin fragments. The main achievement of this work was the development of processes for recovering sodium mannose bisulphite and methyl mannoside from several raw materials. Processes were developed for recovering mannose from crude mixtures via two routes: (1) formation of the sodium bisulphite adducts of monomeric wood sugar mixtures, crystallization and separation of sodium mannose bisulphite and regeneration of mannose from this intermediate, and (2) anhydrous methanolysis concurrent with glycosidation of crude mixed-sugar polymers or monomers, crystallization and separation of methyl xcex1-D mannoside and regeneration of mannose from this intermediate. These procedures for recovering mannose have the drawback that they are very cumbersome to carry out in practice.
Sinner, M, Simatupang, M. H. and Dietrichs, H. H. (xe2x80x9cAutomated Quantitative Analysis of Wood Carbohydrates by Borate Complex Ion Exchange Cromatographyxe2x80x9d, Wood Science and Technology, 1975, pp. 307 to 322) describe a simple automated analytical method for the separation and quantitative determination of sugars from acidic and enzymatic hydrolysates of wood polysaccharides via borate complex ion exchange chromatography. The sugars separated in this way include mannose, fructose, arabinose, galactose, xylose, glucose and disaccharides like xylobiose, cellobiose and sucrose.
GB 1 540 556 (ICI Americas, publ. Feb. 14, 1979) relates to a method of separating mannose from glucose present in aqueous solutions. The starting mixture of glucose and mannose is typically obtained by epimerization of glucose in an aqueous solution. The separation of mannose from glucose is typically carried out using a cation exchange resin in the form of an alkaline earth metal salt, such as in Ca2+, Sr2+ or Ba2+ form. The cation exchange resin is preferably a strongly acid cation exchange resin, typically a resin based on styrene divinylbenzene.
The separation of sugars from lignosulphonates has been described by Hassi, R., Tikka, P. and Sjxc3x6strxc3x6m, E. (xe2x80x9cRecovery of Lignosulphonates and Sugars from Spent Sulphite Liquors by Ion Exclusion Chromatography, 1982 International Sulfite Pulping Conference, Sheraton Centre Hotel, Toronto, Ontario, October 20-22, pp. 165 to 170). Ion exclusion chromatography on a strongly acid cation exchange resin has been applied to the fractionation of lignosulphonates and sugars, including mannose, present in a spent sulphite liquor. The resin used in the tests was a strongly acid gel-type polystyrene cation exchange resin (Amberlite IR-120, Ca2+ form). It is proposed that the sugar fraction might be used as a raw material source for mannitol production.
Finnish Patent 78734 (Suomen Sokeri Oy, publ. Apr. 5, 1987) relates to a multi-step process of separating sugars and lignosulphonates from a spent sulphite pulping liquor. This process comprises introducing a spent sulphite pulping liquor into a chromatographic column including a separation resin in a metal salt form, typically a strongly acid cation exchange resin in a Ca2+ form, eluting the column with water to recover a fraction rich in lignosulphonates and a fraction rich in sugars, introducing the fraction rich in sugars thus obtained into another chromatographic column including a separation resin in a monovalent metal salt form, typically in Na+ form. A sugar fraction free from lignosulphonates is obtained.
WO 96/27029 (Xyrofin Oy, publ. Sep. 6, 1996) relates to a method of recovering an organic compound, such as sugars, from solutions by crystallizing the compound substantially by way of nucleation. It is proposed that mannose can be recovered by the nucleation crystallization process, for example.
Finnish Patent 97 625 (Xyrofin Oy, publ. Mar. 5, 1996) discloses a process for crystallizing xylose. In this process, xylose is recovered by crystallization from solutions in which the xylose purity is relatively low. Especially, this process concerns recovering xylose from biomass-derived solutions.
WO 99/10542 (Cultor Corporation, publ. Mar. 4, 1999) discloses a process of recovering L-arabinose from sugar beet pulp by a chromatographic separation method using a cation exchanger in a monovalent metal form as the separation resin. The L-arabinose solution thus obtained is purified by means of cation and anion exchangers and adsorbent resins.
WO 01/21271 A1 (Sohkar Oy, publ. Mar. 29, 2001) discloses a method of recovering pectin, arabinose and salts from vegetable material using a cation exchange resin, which is preferably in the form of a multivalent metal.
Biomass-derived raw materials used for the recovery of mannose are typically complex multicomponent mixtures. Separation of mannose with sufficient purity from these complex mixtures has presented a problem. One of the problems associated with the above-described known processes is that they provide mannose as a mixture with other closely-related sugars or that they do not provide mannose with a sufficient degree of purity. On the other hand, the production of mannose from mannans and other mannose derivatives is technically very cumbersome. Furthermore, it has been problematical to prepare suitable starting mannose solutions for the crystallization of mannose to obtain a crystalline mannose product.
It has now been found that mannose with high purity can be effectively recovered from biomass-derived carbohydrate-containing solutions using a novel chromatographic separation method. With the chromatographic method of the invention, a mannose fraction having a purity of 45 to 80% or more can be obtained. The mannose fraction obtained from the chromatographic separation can then be further purified by crystallization. The crystallization provides a crystalline mannose product having a purity of up to 99% or more. In connection with the method of the invention, various other sugars, such as xylose and arabinose can be recovered as by-products, depending on the composition of the starting biomass-derived raw material.
It is thus an object of the present invention to provide a method of recovering a mannose product with high purity from carbohydrate mixtures containing the same. As by-products, various other sugars, such as xylose and arabinose can be recovered. The objects of the invention are achieved by a method which is characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea of purifying the mannose-containing carbohydrate mixture chromatographically using at least two separation resins, one of which is Ba2+-based resin.
With the method of the invention, a mannose product with high purity can be obtained.
In the specification and throughout the examples and the claims, the following definitions have been used:
SAC refers to a strongly acid cation exchange resin.
DS refers to a dry substance content measured by Karl Fischer titration, expressed as % by weight.
RDS refers to a refractometric dry substance content, expressed as % by weight.